In a monolithic network architecture, both the data plane (also referred to as the forwarding plane) and control plane are integrated into the same network element. Despite the rapid improvement on line speeds, port densities, and performance, tight coupling of data and control planes in the monolithic network architecture usually results in overly complicated data and control planes and requires complex network management functions to be distributed throughout the network. This creates a huge burden for network operators and equipment manufacturers when adapting the monolithic network architecture for new protocols and results in a high cost barrier for advancing network technology developments.
Unlike the monolithic network architecture, a flow-based, split architecture decouples the forwarding and control functions of the network. In such a split-architecture network, the control and forwarding components of the network are separated, and a flow-centric view of the traffic passing through the network is provided to a centralized flow controller. Examples of networks with such a split architecture includes the access/aggregation domain of carrier-grade networks, mobile backhaul, cloud computing, and optical transport networks (OTN) and wavelength division multiplexing (WDM) networks with multilayer (Layer3 & Layer2 & Layer1) support, all of which are among the main building blocks of modern networks.